1. Field of the Invention
The subject matter of the invention is a process for the bending of metal hollow sections and an apparatus for carrying out the process.
2. Description of the Prior Art
Thus far there is known a so-called core stretching-bending process, which includes by the following characteristics:
A rotatably driven bending pattern is disposed on a tool holder. The section is clamped and bent around this core while applying a traction on the section to be bent.
With such a core stretching-bending process, in which, when using hollow sections, mandrels are taken along in the cavity of the section, it is possible to shape complicated sections with narrow radii.
It is not necessary to fill and to stabilize the hollow section by sand or other support materials.
The core stretching-bending process is used above all when large quantities of workpieces to be bent are demanded, where a bending process in the same direction always takes place successively on the same bending pattern.
Core stretch-bending according to the known prior art is also used whenever the rolling-bending process, also known per se, can no longer be used with narrow radii.
The rolling-bending process involves shaping of a workpiece between bending rollers designed as profile rollers. There may be three or four profile rollers, two lower bending rollers being, as a rule, spaced from each other, and if desired they may be arranged tiltable or pivotable at a housing, and opposite the two lower bending rollers there is a fixed upper bending roller which engages in the space between the two lower bending rollers. The section to be shaped is introduced into the interstice between the upper bending roller and the two lower, mutually spaced bending rollers, it being guided through by a rotational drive of the bending rollers. The shaping then occurs around the upper central roller (bending roller).
In another form of the realization it is known practice to arrange the two lower bending rollers fixed at a machine tool and to design the upper, central bending roller for feed or advance into the interstice between the two lower bending rollers in the direction of the workpiece.
Instead of the three-roller bending machine here described, also the use of a fourth, central bending roller is known, the fourth central bending roller being arranged below the upper central bending roller.
This results in the advantage that the section opposite the upper central bending roller cannot give way downwardly because it is guided and supported by the lower central bending roller.
What is determining here is not the downwardly pointing guidance of the section, but also the lateral guidance, which is achieved by the lower central bending roller.
This rolling-bending process with three or four bending rollers is used whenever relatively large bending radii must be bent depending on section size or respectively small quantities, which also may have different radii.
For the bending of hollow sections with such three- or four-roller bending machines the hollow cross-section must, as a rule, be filled in order to support and stabilize it. This measure of filling the hollow section for the purpose of support during the bending operation takes time and is relatively cost-intensive. Furthermore, filling of the hollow cross-section with a filling material increases the bending resistance and hence also the specific surface pressure on the section now necessary to bend the reinforced section. Thereby flexing phenomena and roll-outs on the hollow section are created, which in turn are undesirable and adversely affect the quality of the bending process.